A compact laser source with low frequency fluctuations is an important component in many applications such as optical communication, spectroscopy, atomic clock, astronomy, and metrology. A key part of a semiconductor laser, directly affecting its stability, is the frequency selective component such as the resonator or the cavity. In semiconductor lasers, the fluctuations in the resonator are mainly caused by thermal variations of the cavity length and index of refraction as well as the elasto-optic effect. Laser stabilization using optical feedback, electrical feedback, and electrical feedforward techniques have been demonstrated. However, the most widely used method in laser stabilization is the Pound-Drever-Hall (PDH) scheme, where the frequency of the laser is measured using an optical frequency reference and the error signal in the electrical domain is amplified, filtered, and fed back to the laser to suppress the laser frequency fluctuations. Bench-top PDH systems have been demonstrated where a high quality factor cavity or resonator in a carefully controlled environment is used to stabilize the laser frequency. Despite excellent stabilization performance, these bench-top systems are bulky, expensive, power hungry, and highly sensitive to environmental fluctuations.
There Standard complementary metal-oxide semiconductor (CMOS) silicon-on-insulator (SOI) processes offer high optical confinement, high yield, scalability to mass production, and co-integration with standard electronic devices and circuits and therefore are a suitable platform for monolithic integration of electronic-photonic systems in the infrared regime.